Fingerprint Activated Door Lock

Featured ProjectsPublished February 25, 2010 at 11:41 pm No Comments

In college we were required to present a project that we worked on every semester. At an engineering school that prides itself on making sure that its students are engaged in hands on work, there was almost always a project that I found was worth presenting. Except, during the second semester of my freshman year. Because of the boring nature of the fundamentals of my education, we did not have anything interesting to present. Therefore, in the few days before our presentation and after our finals period, a couple of friends and myself executed our own creative endeavor. We used a USB fingerprint reader, a computer and a solenoid to make a dorm room lock biometrically activated. The project was completed with three people contributing less than sixty man hours from the start of development to the presentation of our results.  From nothing to done in three days made us pretty proud freshman.

This project is being written up almost three years after its execution so the writeup may be a little hazy.

There were two collaborators on this project: Eamon Doyle and Clark McPheeters.

background

The project started with a silly idea. As freshman at a small engineering college my roommate Eamon and I were always trying to think of creative ways to do something novel. We had heard from the upperclassman at the college about all the crazy things they had done and as the last incoming class prior to our schools first graduation; there might have been some inkling of wanting to also leave a legacy. On a whim, Eamon purchased a few USB fingerprint readers from eBay. Now back then, biometrics were novel. Facial and fingerprint recognition were far from standard gimmickry on laptops, and the notion of password-less protection was so novel that it still seemed like some awesome, super secret, spy-movie worthy way to secure data. However, unlocking a computer with a fingerprint reader is slow and kind of lame. In the movies it was always a combination of biometrics that opened a door. Since we hard these fingerprint readers, we figured that we would give it a try, one biometric at a time.

the SDK

Reading the fingerprints were easy, but the application that came with the readers was only good for filling in passwords. We needed more flexibility than that if we wanted to actually do something. As freshman, we knew nothing about embedded platforms of any kind and the only programming experience that either of us had was on windows PC’s. After unfairly blaming our respective high school computer science departments for that deficiency, we set about looking for a .net SDK (software development kit) that we could use to trigger an external device.Through a little work and a lot of luck, Eamon hit gold. He found a company in Lithuania that thought that we were pretty cool kids and gave us a copy of their thousands-of-dollars-for-sale SDK for free, the only stipulation being that we send them pictures of our application, the story of our project, and put their logo on our poster when we presented. We didn’t know it at the time, but the VeriFace/VeriFinger software would roll out in about a years time as the software behind the IBM/Lenovo biometrics packages.

Once we got the SDK up and running on the PC it was time for me to put my C++ skills to use. Using their demo as a starting point I realized that the easiest way to make the system work would be to use the serial port on the device to output a high string to open the door when a finger was recognized and low string all other times. Looking back, now it seems like a very messy solution, but as a freshman I simply didn’t know any better. After writing a few lines of code and more than a few hours, the app was done, we had a faint but consistent signal output when the system recognized a previously enrolled fingerprint.

The picture above shows the finished software in action. For the most part the GUI from the code example was retained. Databasing and logging features were added in addition to the serial signaling on successful print match.

the hardware

While I was coding the other members of the team, Eamon Doyle and Clark McPheeters were busy making the parts needed to make the system work. The first order of business was to take the lock out of the door. There weren’t rules against this when we were freshman in college…but there were rules against it by the time I was a junior. Views of the disassembled lock are below:

Once the lock was disassembled, a solenoid was selected that would be small enough to fit into the empty space and pull the locking pin on the door lock. One of the design goals was to make sure that the keys for the door still worked in the event that the system stopped functioning, as the system would be running on a Windows machine we thought this to be a neccesary precaution. As freshman, we all learned how to CAD, but for the purposes of conceptual design, things were still done on paper first. We also didn’t want to damage the lock at all, so any mounting would have to be done without screws, glue or brazing. To make it work, Clark and Eamon set about designing a solenoid mount.

As shown by the above placement, a mount that took advantage of the geometry of the case would hold the solenoid in place. We also needed to make a new plate to replace the one that keeps the handle from turning and therefore the door from opening, By actuating that plate we would be able to open the door using both the key or using the solenoid to move the plate. Once the design was set, a CAD model of the lock and new pieces was made to ensure that everything would fit together as planned.

The next step was actually making the pieces. From the CAD design, Clark and Eamon milled the pieces out of aluminum stock. The mount was made first:

As can been seen from the pictures above, the geometry of the mount is precision made so that it can make use of the cuts in the lock to hold the solenoid in place. The next step was to make a replica of the plate that we need to move. We could not modify the original since we would have to restore the lock completely to original condition once we moved out at the end of the year. Photos showing the manufacturing of the plate are below:

Like the mount, this was also milled out of aluminum. Given the training that we had at the time, it was the best choice. It would probably be a good choice again too, if we had the access to the same kind of machinery and could just find small blocks of scrap aluminum stock lying around.

putting it together

Once all the components were made, the lock needed to be reassembled with its new parts and tested. At this point, the software was working, but we knew that we didn’t have the power needed to open the solenoid just coming from the serial port. We knew we would have to take some DC power from the inside of the PC to make it work. What we didn’t know was how much power would be needed to operate the solenoid. Therefore, testing with a power supply served two purposes. Photos of the assembly and the testing are below:

On the first try the testing was successful! All that was left was to present it…and eventually install it on our door!

presentation/epilogue

On the day of the presentation, we were ready to go. Looking back, we were really proud of the work we had done. Most of us had a pretty rough semester; but the world seemed all better now that we felt like we had something pretty cool to present. We took the time to make sure that our poster /demonstration stood out too!

People seemed to think it was pretty novel too. Though I think the facilities workers liked it the most. Their managers were much less thrilled by the latest in alterations to campus equipment. Of course, as soon at it was over; we installed it so that we would use it from the week after our presentation to the date after which we were kicked out of the dorms for the summer.